Investigators are calling the low-intensity Pune serial blasts a case of improvised explosive devices that didn't go off as planned and suspecting the Indian Mujahideen's hand in the terror attack. Rajesh Ahuja & Presley Thomas report. 'Blasts were well planned' | Blasts hit Pune

Investigators are calling the low-intensity Pune serial blasts a case of improvised explosive devices (IEDs) that didn't go off as planned and suspecting the Indian Mujahideen's (IM) hand in the terror attack.

Sources said the IEDs contained shrapnel in a metal container, a paste of ammonium nitrate in oil, a nine-volt battery and a wrist watch as timer. Initial reports suggest they didn't work properly because of dampness.

"The two unexploded IEDs recovered in Pune have been found to be very complex in nature," said a senior union home ministry official.

A senior investigation officer in Pune said the blasts appeared to be the handiwork of IM.

"The explosives were planted to cause maximum damage and leave no scope for the people to escape."

Central and state police agencies investigating the blasts opine that the choice of location and careful planning to set off simultaneous blasts within a period of 45 minutes in a radius of 500 metres indicates that a well-trained hand was behind the attack.

The two lead agencies, the Maharashtra Anti-Terrorism Squad (ATS) and the National Investigation Agency (NIA), investigating the blasts are studying past instances and modus operandi that the terrorist organisation had used in the past.

Maharashtra home minister RR Patil on Thursday said the possibility of the blasts being an attempt to avenge the murder of suspected IM operative Qateel Siddiqui in Pune's Yerawada Jail was being probed.

The Pune police chief, he said, had received a letter threatening retaliation for the murder.

Siddiqui was found murdered in his prison cell in June after a brawl with fellow inmates.

Police sources said the culprits were well versed with Jangali Maharaj Road - where the four blasts on Wednesday occurred within 45 minutes.

The suspicion was on IM also because many of its cadres were from Pune or had studied there.

Only a person who knows the city very well would know that none of the shops or establishments in a plush area like Jangali Maharaj road had CCTV cameras, said police sources.

"Prima facie it does not seem to be a dry run. If one carefully studies the blast sites, the explosives were planted in a manner to cause maximum damage. Ostensibly, it seems to be the handiwork of IM. But there seems to be an error either in the way the explosives were packed or in the detonator, which saved many lives," said a senior police officer, who has been part of various blast investigations, requesting anonymity.

Two explosives were planted near the Bal Gandharva Rangmandir, of which one was on a bicycle and the other one happened to be in the bag of Dayanand Bhaurao Patil. The remaining four explosives were also planted very strategically, said the officer.

Three of the explosives were planted within 100 metres of each other at McDonalds, Dena Bank and outside City Shoes shop, while the fourth explosive was found just opposite the McDonald's restaurant.

"If one analysis the pattern, the persons who planted the bomb had left no scope for people in the area to escape, and wanted to inflict maximum casualty," said the officer.

On Thursday morning a team of National Security Guards post-blast investigation team led by a lieutenant colonel, officials of the National Bomb Data Center and the Director of Central Forensic Science Laboratory Dr Rajendra Singh visited the blast spot outside McDonald's restaurant on Jangli Maharaj road, and collected samples.

Pune isn't the first time the IM has struggled to assemble explosives, police sources said.

IM comes particularly into focus because it is not the first time the terrorist organisation has struggled to assemble explosives, said police sources.

In November 2008, its operatives planted at least two dozen IEDs across Surat in Gujarat but none exploded as the circuits were faulty.

But none of the bombs had exploded due to faulty circuits. Also, four IED's which the IM cadre had planted had not exploded in Uttar Pradesh in 2006.

In 2008, Bangalore city too had witnessed similar low intensity blasts investigations of which led to IM cadre, said police sources.